1. Field of the Invention
The present invention relates to disc drive assemblies, especially for computer hard drives, and to methods for damping disc drive assemblies.
2. Description of the Related Art
Disc drive units are well known in the art as data storage devices capable of storing a large amount of information input into and generated by computers. FIG. 17 shows a conventional disc drive unit 100, such as shown in U.S. Pat. No. 6,529,345 and in U.S. Pat. No. 5,282,100. The disc drive unit includes a housing comprising a top cover mountable over and cooperating with a base 106 to establish an internal, sealed chamber. The cover comprises an inner layer 102 and an outer layer 104. Sealed inside of the chamber is a head-disc assembly comprising one or more circular discs 108 stacked yet spaced apart from one another on a spindle motor hub, which is rotatably driven by a spindle motor (not shown). The spindle motor may be fixed to the base and/or cover of the housing. The head-disc assembly further comprises a plurality of read/write heads 114, with one head 114 provided for each disc 108. The read/write head 114 transfers electronic data between the tracks on the discs 108 and the external environment, e.g., a computer monitor or printer. In the write mode, the head 114 writes data (input through an input source, such as a computer key board or scanner) onto the tracks of the disc 108. In the read mode, the head 114 retrieves stored information from the disc tracks for relaying the information to an output source, such as a display monitor, printer, or other storage medium.
Data and other information are stored over a majority of the surface of the rotatable disc or discs and, accordingly, are not accessible unless the head 114 moves sufficiently to reach a majority of the disc surface. To permit head 114 movement, the disc-head assembly further comprises one or more actuator arms 110 and actuator (e.g., voice coil) motors 112 for moving the head 114 radially across the disc surface to a desired location adjacent the disc surface. Actuator arms and motors may be arranged in a wide variety of designs and configurations known and practiced in the art. In the illustrated device, the actuator arms 110 turn about a pivot bearing assembly. The pivot bearing assembly includes a stationary element such as a pivot journal fixed to the disc drive housing at the base and cover to define and stabilize a pivot axis. The actuator arms 110 move in response to energizing currents sent from the motors 112, which moves the disc-head assembly on the pivot axis, swinging the actuator arms 110 to move the head 114 radially relative to the disc 108 surface.
Movements of the disc-head assembly, and in particular the actuator arms 110, tend to be relatively rapid and may cause the disc-head assembly to vibrate. The vibration tends to be transferred to the disc drive housing. The cover, and in some cases the base, of the disc drive housing commonly have a relative large surface area, which when vibrated, may radiate acoustic noise. In some cases, the cover may act as a speaker-like structure, producing undesirably high levels of acoustic noise. Additionally, operation of the spindle motor and rotation of the discs at high speeds (such as 7200 rpm) and airflow noise generated by the spinning discs contribute to the vibration and noise. Under some operating conditions, the acoustic noise may be sufficient to disturb or aggravate the user.
In order to dampen the vibration and acoustic noise generated during operation of the disc drive unit, the outer layer 104 of the cover may be attached to the inner layer 102 using a mechanical isolation and sound-damping material, such as adhesive coated foam rubber. However, the sound-damping adhesive is not considered sufficient under some operational conditions for adequately attenuating the vibrations and acoustic noise.
Acoustic dampers have also been made from a constraining layer of metal, such as steel, adhered to the surface of the disc drive housing by a viscoelastic damping adhesive. An acoustic damper is disclosed in U.S. Pat. No. 6,536,555, which discloses an acoustic damper comprising a plurality of damping adhesive strips and constraining layers in alternating relationship. The adhesive strips have temperature-dependent damping efficiencies exhibiting optimal damping properties at different temperature ranges from one another. The '555 patent discloses that the constraining layers are preferably made of stainless steel, aluminum, mica, or polycarbonate hard plastic material.
Laminates as described in the '555 patent have several drawbacks. In order to place the viscoelastic adhesive in direct contact with the disc drive housing and maximize performance, the viscoelastic adhesive and the constraining layer are preferably molded or otherwise shaped to match the surface contours of the disc drive housing. However, the use of laminates comprising viscoelastic layers and metallic skins is often accompanied by design tradeoffs. For example, metallic skins and viscoelastic layers generally lack sufficient moldability or malleability to allow them to be fabricated for and mounted, in continuous intimate contact, to disc drive units having complex shapes. Accordingly, parts or portions of a disc drive unit that are not or cannot be associated with a damper layer, for example, due to the complex shape of the device, can adversely affect dampening effectiveness. Although polycarbonate has better moldability than steel, polycarbonate has inferior physical properties, such as a relatively low modulus of dynamic shearing elasticity of about 350,000 psi and a relatively low density of about 1.2 g/cc. Mica likewise has a low density, is highly brittle, and is not readily formable or shapeable into complex shapes.
Accordingly, it would be a significant improvement in the art to provide a disc drive assembly comprising a damper structure that is sufficiently moldable or shapeable to avoid significant design tradeoffs, and possesses desirable physical properties.
3. Objects of the Invention
Accordingly, it is an object of the present invention to provide a damper structure that is readily formable into a desired shape, including a complex shape, for permitting placement of the damper structure in intimate contact with a disc drive unit.
It is another object of the present invention to provide a damper structure having excellent physical properties for damping and withstanding the stresses imparted by a disc drive unit.
It is another object of the present invention to provide a method for damping a disc drive assembly, including a method for making disc drive assemblies that achieve one or more of the above-discussed objects.
It is still a further object of the present invention to provide a method for retrofitting an existing disc drive assembly to include a damper structure according to the present invention.